This application is a U.S. national phase application of International Application PCT/JP99/01063 filed Mar. 5, 1999.
The present invention relates to a silicon steel sheet which is suitable for iron cores used for such as a transformer, a reactor and a motor and a method for producing the same.
It is in general known that iron loss of a silicon steel sheet rises drastically when exciting frequency becomes high. On the other hand, driving frequency of such as a transformer, a reactor and a motor for which the silicon steel sheet is widely used has recently been made yearly to be of higher frequency in order that an iron core is made to be compacted and to be highly efficient.
Accompanied by this driving frequency being made to be of higher frequency, a case that temperature rise and efficiency deterioration of these iron cores owing to iron loss of the silicon steel sheet invite a problem is remarkably increasing. For such reason, it has become demanded that high frequency iron loss of the silicon steel sheet is reduced.
As conventional method of reducing high frequency iron loss of the silicon steel sheet, a method of reducing high frequency iron loss by increasing resistivity by means of increasing Si content in the silicon steel sheet and a method of reducing high frequency iron loss by suppressing eddy current loss by means of thinning sheet thickness have been employed.
Since the method of increasing Si content in the silicon steel sheet, however, among the above described conventional technologies, deteriorates formability of the silicon steel sheet remarkably, there is a problem that not only deterioration of productivity of the silicon steel sheet itself is invited but also increase in cost for producing iron cores is invited.
On the other hand, so far as the method of thinning the sheet thickness is also concerned, the thinner the sheet thickness is, the more cost for producing the steel sheet itself increases, and still further more increase in cost for producing a core is invited since a piling number of sheets increases. Thus, there is also a problem which the method of thinning the sheet thickness has.
In response to the above circumstances, siliconizing method has been developed as a method of producing a high Si steel sheet which is poor in formability and in particular a 6.5% silicon steel sheet excellent in magnetic properties is produced. According to the siliconizing method, it means technology in which after a low silicon steel plate has been rolled into a silicon steel sheet, Si is made to be permeated and diffused from surface of the steel sheet.
Recently, however, an electric appliance has remarkably been made to be of higher frequency and a material which has lower iron loss than a 6.5% silicon steel sheet has been demanded.
It is an object of the present invention to provide a silicon steel sheet having low iron loss of high frequency and a method for producing the same.
To attain the object, firstly, the present invention provides a silicon steel sheet having low iron loss of high frequency which comprises:
a steel sheet surface layer and a steel sheet center portion;
the steel sheet surface layer having Si concentration higher than Si concentration of the steel sheet center portion;
Si concentration of steel sheet center being 3.4 wt. % or more; and
Si concentration of the steel sheet surface layer being 5 wt. % or more.
Secondly, the present invention provides a silicon steel sheet having low iron loss of high frequency which comprises:
a portion of at least 10% from both of upper surface and lower surface of a steel sheet in sheet thickness direction having Si concentration of 5 to 8 wt. %; and
Si concentration in the vicinity of sheet thickness center being at least 3.4 wt. %.
Thirdly, the present invention provides a silicon steel sheet having high saturation magnetic flux density and low iron loss of high frequency which comprises:
a steel sheet having a Si concentration gradient in sheet thickness direction;
the steel sheet having a surface layer and a steel sheet center portion, the surface layer having Si concentration higher than Si concentration of the steel sheet center portion; and
an average Si concentration being 3.5% or less in sheet thickness direction of the steel sheet.
Fourthly, the present invention provides a soft magnetic strip having low iron loss of high frequency which comprises:
a strip having a surface and a center portion; and
a magnetic permeability of the surface having two times or more of a magnetic permeability of the strip center portion.
Fifthly, the present invention provides a soft magnetic strip having low iron loss of high frequency which comprises:
a soft magnetic strip comprising a silicon steel sheet having a Si concentration gradient in thickness direction and having a strip surface and a strip center portion; and
a magnetic permeability of the strip surface having two times or more of a magnetic permeability of the strip center portion.
Sixthly, the present invention provides a silicon steel sheet having low iron loss of high frequency which comprises:
Si concentration in a surface layer portion of 10% or more from both of upper surface and lower surface of a steel sheet in sheet thickness direction being 5 to 8 wt. %; and
Si concentration in the vicinity of sheet thickness center being 2.2 to 3.5 wt. %.
Seventhly, the present invention provides a silicon steel sheet having excellent in magnetic properties of high frequency which comprises:
a silicon steel sheet having a Si concentration gradient in sheet thickness direction and having a surface layer and a steel sheet center portion;
the surface layer having Si concentration higher than Si concentration of the steel sheet center portion;
a difference between a maximum and a minimum of Si concentration in sheet thickness direction being 0.3 wt. % or more;
Si concentration of the surface layer being 5 to 8 wt. %; and
a difference between front surface layer and back surface layer being 1 wt. % or less.
Eighthly, the present invention provides a method for producing a silicon steel sheet having excellent magnetic properties of high frequency, which comprises the steps of:
performing simultaneously siliconizing treatment of penetrating Si from a steel sheet surface and diffusing treatment of diffusing the penetrated Si in a steel sheet in non-oxidizing atmosphere which includes Si compound; and
controlling velocity of siliconizing and diffusing so that Si concentration of a surface layer is higher than Si concentration of a sheet thickness center portion, a difference between a maximum and a minimum of Si concentration in sheet thickness direction is 0.3 wt. % or more, Si concentration of the surface layer is 5 to 8 wt. % and a difference between front surface layer and back surface layer is 1 wt. % or less.
Ninthly, the present invention provides a method for producing a silicon steel sheet having excellent magnetic properties of high frequency, which comprises the steps of:
subjecting a steel sheet to siliconizing treatment in non-oxidizing atmosphere which includes Si compound;
performing diffusing treatment of Si in non-oxidizing atmosphere which does not include Si compound; and
controlling velocity of diffusing in the step of the performing the diffusing treatment so that Si concentration of a surface layer is higher than Si concentration of a sheet thickness center portion, a difference between a maximum and a minimum of Si concentration in sheet thickness direction is 0.3 wt. % or more, Si concentration of the surface layer is 5 to 8 wt. % and a difference between front surface layer and back surface layer is 1 wt. % or less.
Tenthly, the present invention provides a grain-oriented silicon steel sheet having low iron loss, which comprises:
a sheet thickness of 0.2 mm or more;
C in an amount of 0.01 wt. % or less;
Si concentration in a surface layer portion of 10% or more from both of upper surface and lower surface of a steel sheet in sheet thickness direction being 5 to 8 wt. %; and
Si concentration in the vicinity of sheet thickness center being 2.2 to 3.5 wt. %.
Eleventhly, the present invention provides a grain-oriented silicon steel sheet having low iron loss, which comprises:
a sheet thickness of less than 0.2 mm;
C in an amount of 0.01 wt. % or less;
Si concentration in a surface layer portion of 10% or more from both of upper surface and lower surface of a steel sheet in sheet thickness direction being 5 to 8 wt. %; and
Si concentration in the vicinity of sheet thickness center being 3 to 6 wt. %.
Twelfthly, the present invention provides a silicon steel sheet having excellent magnetic aging property and residual magnetic flux density, which comprises:
0.003 wt. % or less C, 0.05-0.5 wt. % Mn, 0.01 wt. % or less P, 0.02 wt. % or less S, 0.001-0.06 wt. % sol. Al and 0.01 wt. % or less N;
an average Si of 7 wt. % or less; and
the steel sheet having a Si concentration gradient in sheet thickness direction, Si concentration of a surface layer being higher than Si concentration of a sheet thickness center portion and a difference between a maximum and a minimum of Si concentration being 0.5 wt. % or more.
Thirteenthly, the present invention provides a method for producing a silicon steel sheet, which comprises the steps of:
performing siliconizing treatment of penetrating Si from a steel sheet surface and diffusing treatment of diffusing the penetrated Si in a steel sheet in the same furnace and in the same gaseous atmosphere; and
controlling velocity of siliconizing and diffusing by means of controlling treatment time and treatment interval for the siliconizing treatment and the diffusing treatment to control Si concentration distribution in steel sheet thickness direction.
Fourteenthly, the present invention provides a method for producing a silicon steel sheet, which comprises the steps of:
performing simultaneously siliconizing treatment of penetrating Si from a steel sheet surface and diffusing treatment of diffusing the penetrated Si in a steel sheet in the same atmosphere; and
controlling velocity of siliconizing and diffusing to control Si concentration distribution in steel sheet thickness direction.